High-frequency induction furnace



July 16, 1929. r w. ESMARCH -1,721,073

HIGH FREQUENCY INDUCTION FURNACE Filed octr 12, 192 2 Sheets-Sheet 1July 16, 1929. w. ESMARCH HIGH-FREQUENCY INDUCTION FURNACE Filed Oct.12, 1927 Shets-Sheet '2 Patented July 16, 1929.

UNITED STATES PATENT OFFICE.

'WILHELM ESMARCH, OF BERLIN-HALENSEE, GERMANY, ASSIGNOR TO SIEMENS &HALSKE, AKTIENGESELLSCHAFT, OF SIEMENSSTADT, NEAR BERLIN, GERMANY, A.

CORPORATION OF GERMANY.

HIGH-FREQUENCY INDUCTION FURNACE.

Application filed October 12, 1927, Serial No. 225,620, and in GermanyJune 10, 1927.

This invention relates to primary windings for high frequency inductionfurnaces. Such windings have heretofore been mad of watercooledcopper'tubes or even of comp. ratively thick copper bands. In windingsof this kind however the influence of the skin effect is highlydetrimental, the currents on the inside of the conductor becomingcrowded together so that the major part of the cross sectional area ofthe'conductor is not used for carrying the current, and the efliciencyfactor of the furnace is lowered. In the smelting of metals for exampleit has not been possible, owing to the conductivity say of the iron toraise such factor above 70%. It would be still ower if instead of asingle layer of windings several such layers were employed.

According to the present invention this disadvantage is overcome bydividing the primary winding into two or more bands set up on edge andinsulated from each other, the

thickness of the several bands being so proportioned that the influenceof the skin effect 1s no longer noticeable and the cross sectional areais completely utilized for conducting the current, and the severalwindings being so arranged and shaped as to be alike in respect ofresistance, impedance and inductive action on the interior of thefurnace.

The accompanying drawings illustrate several constructional examples ofthe subject matter of the invention with bands arranged in a number oflayers.

Fi 1 is a vertical section of a crucible with one orm of my improvedprimary winding coiled around it; Figs. 2, 3 and 4 are diagrammaticviews showing in development and on a smaller scale than Fig. 1, threedifferent forms of coils or winding embodying the invention, the coilshown in Fig. 4: corrcsp0nding to that shown in Fig. 1; Fig. 5 is adetail perspective view of a portion of a coil made in accordance withFig. 2; Fig. 6 is a vertical section of a crucible with another form ofmy improved coil; and Fig. 7 is a diagrammatic developed viewillustrating de- 4 tails of the coil shown in Fig. 6.

Figure 1 shows in vertical section a crucible t, around which aconductor of the novel type is helically coiled. This conductor may,consist of two three or four layers of thin copper strips. Figs. 2, 3and 4 are diagrammatic plan views or developed views representing coilsor windings embodying two, three, and four layers respectively, andshowing the conductors or strips composing said coils, in the conditionin which they appear before the are formed into coils. The winding orcoil shown in Fig. 1 is represented as having four lar furnace. Thethickness is proportion a,

to the square root of the frequency so that this latter for a frequencyof 10,000 would be only th of the thickness of the conductor for afrequency of 100. For these frequencies of 10,0C0 and 100 the stripswould have thicknesses of, say, 0.67 and 6.7 millimetres respectively.

The copper bands or strips a, b or a, b, 0-

or a, b, 0, d forming the conductors are connected 1n parallel, theirends or terminals 2,, 2, being connected to the source of eurrent. Saidbands or strips are insulated fromeach other throughout their length asby a coating of enamel for example. By arranging suitable distancepieces between them, air insulation may be provided for. Finally stripsof insulating material are placed between the bands or strips.

The bands are crossed at one or more points in such a way that each ofthem will be similar to the others and will have portions in differentpositions at different parts of its length. As shown in Figure 2 acrossing point 6, is provided forthe bands (1 and b and each of themlies for one half of its length on the inside and for the other half ofits length on the outside As shown in Figure3 conductors a, b, careprovided which are crossed at two points .9, in such a way that eachconductor has one-third of 'its length on the inside, one-third in themiddle and one-thirdon the outside of the entire conductor or coil. Asshown in Figure 4 four conductors a, b, 0, d are used, which are crossedat three points 8 in such a way that each band assumes a differentposition at each one-fourth portion of its total length. In thisarrangement of crossings all the parts of the several bands areconnected in series and the current therefore flows in the samedirection at all portions of the total cross sectional area.

In Figure 5 is shown in perspective a con structional example for thecrossing 8 shown in Figure 2. The conductor band I) is turned verticallyupwards on a line is lying at an angle of degrees. The connection member0 thus formed is again turned downwards in a curved form and againturned over obliquely so that the conductor portion 12 runs on at thesame level with b but in a plane parallel thereto. Between the twoportions a and a of the conductor lies the band a, which is connected bya member '0 to a band portion a lying in front of the part b of theconductor. In the constructional example shown in Figures 3 and 4 threeor four connecting members respectively are required. After the wholeconductor with its crossed portions has been produced and the severalbands connected at their ends a coil or winding of the type shown inFigure 1 will be produced, said figure (like Fig. 4) illustrating awinding or coil composed of four bands.

Instead of the minimum number of crossing points indicated in Figures 2and 4 a greater number thereof may be employed. The number of thevarious conductor bands may also be increased. Finally it sufiices formany purposes to use even a single band if it be wound in a suitablenumber of layers like a coil and possesses the cross sectional areaindicated, which gives the maximum current utilization with a minimumskin effect.

In Figures 6 and 7 is shown another constructional example in which theseveral conductors are connected in series, Figure 6 shows acrucible-like hearth '25 around which band-shaped conductors are woundin three turnsor rings I, II, III of three layers e, f, g each. Theseveral turns of the bands are indicated between the supply terminals 22 as shown in Figure 6, and are connected in series in suchv a way thatthe current flows through in the uppermost ring I in the outer conductore, while in the next ring II the current flows in the middle conductor fand in the third ring III in the inner conductor g. From this latter thecurrent then passes into the inner conductor f and so on until itfinally leaves the outer layer 00f the winding in the lower winding IIIthrough the terminal .2

In Figure 7 the connections of the individual windings are shownseparately on a larger scale. These are produced by doubly bending overthe conductor bands which at the cross-over points u consequently passfrom one ring to another and also from one plane to another, while onlyone transfer to another layer of windings takes place at the connectingpoints '0 at the outer sides of. the uppermost and lowermost rings I andIII respectively.

The arrangements shown enable the efliciency factor of the highfrequency furnace to be increased to about 90 to 95 per cent. Thearrangement can also be adapted with the same efficiency for crucibleswhich are not exactly cylindncal, provided the ohmic resistance andimpedance and also the inductive action on the interior of the furnacebe equal all over.

In order to secure a fine equalization of th course of the current inthe action on the secondary circuit any desired kind of parallel andseries connections of the band shaped conductors may be used, employingif necessary at the same time the arrangements shown in Figures 2 to 4and Figure 6.

What I claim as my invention and desire to secure by Letters Patentis 1. A high frequency furnace comprising a crucible and a primary coilinductively associated therewith, said coil comprising a plurality ofthin bands of conducting material set on edge, insulated from each otherand arranged to form a laminated structure, the width and thickness ofeach band being so proportioned relatively to the strength andfrequency, respectively, of the current that objectionable skin effectswill be minimized and the full cross sectional area of the conductors ofthe coil will be substantially completely utilized.

2. A high frequency furnace comprising a crucible and a laminatedprimary coil inductively associated therewith, each conductinglamination of said coil consisting of a plurality of substantially equallengths of a plurality of thin bands of conducting material,

set on edge and connected in series with substantially equal lengths ofthe bands of each of the other lamination of said coil.

3. A high frequency furnace comprising a crucible and a primary coilinductively associated therewith, said .coil consistin of a plurality ofthin conducting insulated ands set on edge and arranged to form alaminated coil structure in which each lamination of the coil consistsof ,a plurality of substantially equal lengths of each of said bands.

4. A high frequency furnace comprising a crucible and a primary coilinductively associated therewith, said coil consisting of a' pluralityof insulated thin bands of conducting material set on edge, connected inparallel and forming a laminated structure, each band consisting of aplurality of serially connected portions, each arranged at a differentdistance from the axis of the coil than its adjacent portions, and sothat each band will have a substanti ally equal length thereof arrangedat the same distance from the axis of the coil band will havesubstantially the same electrical efiect on the interior of the furnace.

5. A high frequency furnace comprising a crucible and a primary coilinductively associated therewith said coil consisting of a plurality 'ofinsulated thin bands of conducting material set on edge and connected attheir ends in parallel, each band consisting of a plurality of portionsarranged in step-like formation at difierent radial distances from theaxis of the coil, each of such portions of each band being substantiallyin line with a pair of adjacent portions of adjacent bands, and theadjacent portions of each band being connectedin series by cross oversections to avoid contacting engagement between adjacent bands.

6. A high frequency furnace comprising a crucible and a primary coilinductively associated therewith, said coil consisting of a plurality ofcontinuous thin bands of conducting material set on edge and connectedat their ends in parallel and being insulated from each other throughouttheir length, each bandconsisting of a plurality of portions ar-' rangedin step-like formation at diflI'erent radial distances from the axis ofthe coil, and

such portions of each band being so arranged relatively to the portionsof the other lamlnations that the coil consists of a plurality oflaminated helical turns, in which each lamination consists of aplurality of portions of different bands.

In testimony whereof I aflix my si ature. WILHELM ESMA CH.

